The use of fluid-filled attenuators in vehicular braking systems is well known. Their use is particularly prevalent in anti-lock brake systems (ABS) at the outlet end of the ABS hydraulic pump used to generate the supplemental brake fluid pressure required to actuate the brakes at the wheel cylinders through the ABS hydraulic control unit and independently of the brake pedal being actuated by the operator. The attenuator assists in significantly reducing the amplitude of the brake fluid high energy pressure pulses at the output end of the pump, thereby helping to eliminate or substantially reduce the mechanical noise hydraulically generated in the braking system and sounding through the master cylinder or its connection to the vehicle. These pressure spikes can be in the order of 900-1000 psi. Use of a conventional attenuator at the output end of the ABS pump will reduce these spikes to about 100-300 psi.
A conventional attenuator, as assembled, basically has no moving parts. It basically comprises a closed chamber filled with brake fluid having an inlet from the output side of the pump and an outlet in an orifice of substantially reduced diameter. Because of the restriction of flow through the orifice, the pressure fluctuations are attenuated as a result of the compressibility of the brake fluid itself. i.e. absorbing the high energy fluid pulses and slowly releasing it through the orifice.
A conventional attenuator used for this purpose is as shown in FIG. 3 herein and described in the detailed discussion appearing below. One notes that the conventional attenuator is of significant axial length as is required to (i) facilitate several O-ring seals confining the brake fluid to the attenuator and assuring its prescribed flow through the attenuator, and (ii) assure the isolation of the incoming fluid to the attenuator reservoir and through the outlet orifice, thereby avoiding any short circuiting of the function of the attenuator. This conventional design also requires a bleed port and fitting for allowing a means of eliminating entrapped air from the brake fluid line. It also requires a compression spring for maintaining the attenuator cylinder firmly against a retaining clip, holding the cylinder in fixed position relative to the hydraulic control unit.